Herz
-
The beta-adrenergic receptors of the myocardium play an important role in the regulation of heart function. The beta-adrenergic receptors belong to the family of G-protein coupled receptors. Three subtypes have been distinguished (beta1-, beta2-, and beta3-adrenoceptors). The receptors consist of seven membrane-spanning domains, three intra- and three extracellular loops, one extracellular N-terminal domain, and one intracellular C-terminal tail. ⋯ In patients with dilated cardiomyopathy the beta-adrenergic responsiveness of the myocardium is diminished. It was shown that in these patients the expression of the beta1-adrenergic receptor is reduced on the mRNA and protein level. In these patients the expression of the inhibitory G-protein G(i) is increased. Furthermore, the expression of the G-protein receptor kinase is elevated. This kinase induces the uncoupling of the beta-adrenergic receptors. These alterations of the beta-adrenoceptor signal cascade may be induced by an elevated catecholamine release or by agonist-like autoantibodies directed against the beta1-adrenergic receptor found in patients with dilated cardiomyopathy. Both, permanent stimulation with catecholamines and chronic treatment with agonistic anti-beta1-adrenoceptor autoantibodies cause a reduction of the expression of the beta1-adrenoceptor on mRNA and protein level in "in vitro" experiments. Moreover, an over-expression of the beta1-adrenoceptor, the stimulatory G(s) protein, and the protein kinase A induce detrimental alterations of the cardiac function and morphology in transgenic animals. These animals developed heart failure accompanied by an increased mortality rate.
-
Fabry disease is an inherited lysosomal storage disorder caused by deficiency of the enzyme alpha-galactosidase A. The enzyme deficiency results in accumulation of glycosphingolipids in the lysosomes n nearly all cell types and tissues leading to a multisystem disease. MANIFESTATIONS include painful crisis, angiokeratomas, corneal dystrophy, and hypohydrosis. The severe renal, cerebrovascular, and cardiac involvement is predominantly responsible for premature mortality in Fabry patients. The disease is X-linked and manifests primarily in hemizygous males but also heterozygous females can be affected. CARDIAC INVOLVEMENT is frequent in Fabry disease. Patients develop hypertrophic cardiomyopathy, arrhythmias, conduction abnormalities, and valvular abnormalities. Although Fabry disease leads to a complex clinical syndrome, there are studies indicating that manifestations can be limited to the heart. The isolated cardiac variant of Fabry disease seems to be more common than previously thought: around 3-6% of male patients with left ventricular hypertrophy seem to suffer from this disease variant. ⋯ Recent advances in molecular biology and genetic engineering have enabled the development of enzyme replacement therapy in Fabry disease. Results from two independent therapy studies are indeed promising: Infusion of the enzyme preparation seems to be well tolerated and effective in catabolizing the lipid deposits. This enzyme replacement therapy could be one of the first examples for causal treatment of left ventricular hypertrophy. Therefore, early diagnosis of hypertrophy patients with the cardiac variant of Fabry disease is important.